This invention relates to the recovery and disposal of waste streams generated in an unsupported slurry catalyst process which is utilized for the hydroconversion of heavy hydrocarbonaceous black oil. It particularly relates to a process for the removal of carbon or carbon compounds from a waste stream which comprises vanadium sulfide, nickel sulfide and carbon or carbon compounds.
High metal content hydrocarbons are unsuitable for hydrotreating in a conventional fixed bed hydrotreater because the metals are deposited on the catalyst at a rapid rate which not only physically plugs the flow of the reactants through the reaction zone but masks the small catalytic sites on the catalyst, thus precluding long, uninterrupted operation of the hydrotreater which is highly disruptive of the entire processing complex of which the hydrotreater is a small but important part. The prior art describes processes which are much more adaptable to the hydrotreating of high metals hydrocarbons. In general, a facile method for hydrotreating high metals hydrocarbons is via a catalyst slurry process whereby the hydrocarbon is admixed with hydrogen and a finely divided metal catalyst or metal catalyst precursor and subjected to elevated temperature and pressure in a reaction zone. The reaction zone effluent is separated to yield a hydrotreated hydrocarbon and a sludge or waste stream containing asphaltenes and at least one metal sulfide. At least a portion of this sludge is usually recycled within the process to provide slurry catalyst for the reaction. In order to prevent an undesirable accumulation of refractory hydrocarbonaceous substances and recovered metal compounds, a dragstream is withdrawn from the process. The dragstream generally comprises carbon or carbon compounds and at least one metal sulfide and is from about 1 to about 10 weight percent of the fresh feed stream to the slurry process. Once the dragstream is removed from the process, it must be utilized or discarded. An attractive method to utilize the dragstream is to remove the carbon or carbon compounds completely and recover the metal values which remain.
The prior art has suggested the removal of carbon or carbon compounds from such a dragstream by high temperature oxidation of the carbon or carbon compounds with air or an oxygen-containing gas. This procedure converts the metal sulfides to metal oxides. Generally, the recovery and use of metal is easier and less expensive if the metal ore is in the sulfide form rather than the oxide form. A preferred method therefore would be to recover the metal values in the sulfide form which makes the subsequent separation and use of the metals more convenient.